Stain-free paper



United States Patent 3,250,619 STAIN -FREE PAPER Donald G. Yunglrurth and William Kerr, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed June 25, 1962, Ser. No. 205,098 13 Claims. (Cl. 96-85) This invention relates to photographic. paper, and more particularly to stain-free photographic paper.

Staining of photographic paper may be caused by the presence of oxidized developer thereon. This problem is especially serious with papers developed by a monobath process. In this process, no attempt is made, such as washing, to remove any developer which remains on the print.

One object of our invention is to provide photographic papers which are resistant to staining caused by oxidized developer. Other objects of our invention will appear herein.

We have found that photographic papers having a surface size thereon comprising styrene-maleic anhydride copolymer and boric acid are highly resistant to stain caused by oxidized developer. We have also found that the presenceof diepoxide resin or other like cross-linking agent enhances the resistance of the styrene-maleic anhydride copolymer-boric acid size to penetration of the paper by developer.

The styrene-maleic anhydride copolymer materials which are useful in accordance with our invention for sizing photographic paper are water insoluble but alkali soluble and thus are first brought into solution in an alkaline material such as aqueous ammonia. This solution can be applied as a sizing coating to the paper which coating tends to prevent penetration of the developer into the paper. The presence of diepoxide resin in the sizing coating increases its resistance to penetration by developer.

The styrene-maleic anhydride copolymer which is employed as a sizing material applied to the surface of the paper is one obtained by the polymerization of styrene with maleic anhydride forming a styrene-maleic anhydride copolymer having the structure:

0 112-0 HC HO H lflHs 0 O \O Instead of the styrene-maleic anhydride copolymer, there may also be employed a partial ester of a polymer of this type such as one in which there is preferably approximately at least one acid group and up to one ester group on the maleic acid unit per styrene unit, some of the carboxyl resulting from converting anhydride to acid having been reacted with alcohol such as methyl, ethyl, propyl, or butyl alcohols. The structure of such a partial ester copolymer is represented by:

R being lower alkyl. It is usually preferable that the styrene maleic anhydride copolymer and the partially esterified styrene-maleic acid copolymer be employed in admixture with each other in any desired portion, preferably equal parts of each. Satisfactory sizes result from the use of sizing solutions containing a total of 14% of the styrene-maleic copolymers. This results in 0.ll.4% of the styrene-maleic copolymers, based on the dry weight of the paper. Especially good results are obtained from sizing solutions containing 2% of the styrene- I is subjected to subsequent heat treatment.

3,25,5l9 Patented May 10, I966 ice I maleic anhydride copolymer and 2% of the partially esterified styrene-maleic acid copolymer, which results in amounts of 0.61.2% of these copolymers, based on the dry weight of the paper.

Good results may be obtained with sizing solutions containing 0.5-4% boric acid, which results in amounts of 0.051.4% boric acid, based on the dry weight of the paper. We prefer to use sizing solutions containing about 3% boric acid, which produces papers containing O.41.0% boric acid, based on the dry weight of the paper.

In the sizing of paper with styrene-maleic anhydride and partially esterified styrene-maleic acid copolymers and boric acid in accordance with our invention, it is desirable in some cases to incorporate therewith a small amount of a nonaldehydic material which will promote cross-linking in the sizing operation. We have found that the presence of a small amount of a polyepoxide resin is very effective in causing cross-linking of the styrene-maleic copolymer sizing materials when the paper An epoxide resin which has been found to be useful for this purpose is the reaction product of bis-phenol-A and epichlorohydrin referred to as Polyether D in U.S. Patent 2,913,356 of Schroeder. This material is indicated to be substantially 2,2-bis(2,3-epoxypropoxy-phenyl)propane. Other polyepoxide resins referred to in the Schroeder patent are useful for promoting the cross-linking of the styrenemaleic copolymers employed in accordance with our invention, particularly those referred to by letter such as Polyethers A, B, C, D and E. The resinous polymeric epoxide compounds useful as catalysts in styrene-maleic copolymer sizing materials are commonly prepared by condensing a polyhydroxy compound such as polyhydric alcohol or a polyhydric phenol with epichlorohydrin. For instance, a resinous polymeric epoxide resulting from the condensation of an epichlorohydrin and a polyhydric phenol is eminently useful in this connection.

Paper having a size thereon as described in accordance with our invention may then be coated with an ordinary gelatino-silver-halide emulsion to produce a photographic paper which is highly resistant to staining caused by the oxidation of any developer which may remain on the paper after the developing operation.

Paper sized in accordance with this invention may also be coated with gelatin or other vehicles containing physical development nuclei to produce a highly stain resistant positive sheet for physical development of an image in solvent transfer systems. The development nuclei used in the sensitive elements of the invention are those physical development nuclei for dissolved silver salts which are Well known in the art including colloidal heavy metals, e.g., colloidal silver and gold; colloidal metal sulfides, selenides and tellurides, e.g., lead sulfide, nickel sulfide, cadmium sulfide, silver sulfide, copper sulfide, zinc sulfide, mercury sulfide; metal protienates, e.g., silver protienates; compounds forming physical development nuclei with dissolved silver salts, e.g., sodium sulfide, colloidal sulfur, organic sulfur compounds such as thiourea, mercaptans and xanthates.

Or invention will be further illustrated "by the following example:

Example 1 A roll of paper base stock weighing 21 pounds per 1,000 square feet was tub sized with an aqueous solution containing 2.4% aqueous (28%) ammonia; 2% of a styrene-maleic anhydride copolymer; 2% of 'a styrenemaleic acid copolymer, part of the carboxyl of which had 3 been esterified with lower alkyl groups; 3% boric acid, and 0.2% of a diepoxide resin (Polyether D of US. Patent 2,913,356). The paper thus obtained was dried and calendered. The paper contained approximately 06-12% of styrene-maleic copolymers and about 0.4-% boric acid. This paper was employed as a support for an ordinary fine-grain, gelatino-silver chloride emulsion which was exposed and processed in an ordinary monobath system. The print was aged for several days and was found to be free of any stain.

The following example illustrates the use of a paper without the sizing of the invention:

Example 2 Example 3 A roll of paper weighing 21 pounds per 1,000 square feet was tub sized with an aqueous solution containing 2.4% aqueous (28%) ammonia; 2% of a styrene-maleic anhydride copolymer; 2% of a partially esterified styrenemaleic acid copolymer; and 3% boric acid. The paper obtained was dried and calendered. The paper contained approximately 0.6-1.2% of styrene-maleic copolymers and about 0.4-1.0% boric acid. This paper was coated with a gelatin solution containing zinc sulfide nuclei and was employed as the positive receiver in a solvent transfer system which made use of monobath processing. After being aged for several days, no stain was found on the print.

Example 4 Paper base which was not tub sized as in Example 3 was coated with the same nuclei dispersion as used in Example 3. After processing as in Example 3 and aging for several days, a heavy yellow-brown stain appeared.

The invention has been described in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected Within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic element comprising paper surface sized with 0.05-1.4%, based on the dry weight of the paper, of boric acid and 0.1-4% of a copolymer selected group consisting of a gelatin silver halide emulsion and a colloid layer containing physical development nuclei for dissolved silver salts, said boric acid being present in the copolymer in a concentration to eifectively prevent staining of the paper when the paper contacts oxidized developer.

6. A photographic element comprising paper surface sized with 0.1 to 1.4 percent, based on the dry weight of the paper, of a copolymer selected from the group consisting of styrene-maleic anhydride copolymer and styrene-maleic anhydride copolymer part of the carboxyl of which has been esterified with a lower alkyl group, and 0.05 to 1.4 percent, based on the weight of the paper, of boric acid, said sized paperhaving a coating thereover selected from the group consisting of a gelatin silver halide emulsion and a colloid layer containing physical development nuclei for dissolved silver salts.

7. A photographic element comprising paper surface sized'with 0.1 to 1.4 percent, 'based on the dry weight of the paper, of a cross-linked copolymer selected from the group consisting of styrene-maleic anhydride copolymer and styrene-maleic anhydride copolymer part of the carboxyl of which has been esterified with a lower alkyl group, and 0.05 to 1.4 percent, based on the weight of the paper, of boric acid, said sized paper having a coating thereover selected from the group consisting of a gelatin silver halid emulsion and a colloid layer containing physical development nuclei for dissolved silver salts.

8. A photographic element comprising paper surface sized with 0.1 to 1.4 percent, based on the dry weight of the paper, of a copolymer selected from the group consisting of styrene-maleic anhydride copolymer and sty- 4. Claim 3 wherein the copolymer contains a polyepoxide cross-linking agent. 5. A photographic element comprising paper surface sized with boric acid and a copolymer selected from the .group consisting of styrene-maleic anhydride copolymer and styrene-maleic anhydride copolymer part of the carboxyl of which has been esterified with a lower alkyl group, and having a coating thereover selected from the rene-maleic anhydride copolymer part of the carboxyl of which has been esterified with a lower alkyl group, said copolymer being cross-linked with the condensation prod uct of epichlorohydrinwith a compound selected from the group consisting of a polyhydric alcohol and a polyhydric phenol, and 0.05 to 1.4 percent, based on the weight of the paper, of boric acid, said sized paper having a coating thereover selected from the group consisting of a gelatin silver halide emulsion and a colloid layer containing physical development nuclei for dissolved silver sa ts.

9. A photographic element comprising paper surface sized with 0.6 to 1.2 percent, based on the dry weight of the paper, of a copolymer selected from the group consisting of styrene-maleic anhydride copolymer and styrene-maleic anhydride copolymer part of the canboxyl of which has been esterified with a lower alkyl group, said copolymer being cross-linked with the condensation product of epichlorohydrin with a compound selected from the group consisting of a polyhydric alcohol and a polyhydric phenol, and 0.4 to 1.0 percent, based on the weight of the paper, of boric acid, said sized paper having a coating thereover selected from the group consisting of a gelatin silver halide emulsion and a colloid layer contailning physical development nuclei for dissolved silver sa ts.

10. Paper surface sized with a mixture of boric acid and a copolymer selected from the group consisting of styrene-maleic anhydride copolymer and styrene-maleic anhydride copolymer, part of the carboxyl of which has been esterified with a lower alkyl group.

11. Claim 10 wherein the copolymer has incorporated therein a nonaldehydic cross-linking agent.

12. A method of preparing a highly stain resistant paper which comprises tub sizing the paper with an aqueous alkaline solution containing boric acid and a copolymer selected from the group consisting of styrenemaleic anhydride copolymer and styrene-maleic anhydridecopolymer, part of the carboxyl of which has been esterified with a lower alkyl group.

13. Claim 12 wherein the sizing solution contains therein a small amount of a nonaldehydric cross-linking agent.

(References on following page) References Cited by the Examiner 3,096,231 7/ 1963 Griggs et a1. 9685 X ED PA ENTS 3,103,462 9/1963 Griggs (it al. 9685 X UNIT STATES T 3,132,944 5/1964 Griggs et a1.

9/ 1945 MacKenz1e et a1 9685 9/1948 Glick 96 85 X 5 FOREIGN PATENTS 10/1949 Harsh et a1 9656 701,051 12/1953 Great Britain.

3/1956 Griggs et a1. 9685 8/ 1956 Griggs et a1. 9685 NORMAN G. TORCHIN, Primary Examiner. 11/1959 Schroeder 117-155 10/1961 Bishop et a1. 117 -155 STONE Examme" 11/ 1962 Crawford 96 76 10 I. RAUBITSCHEK, Assistant Examiner. 

1. A PHOTOGRAPHIC ELEMENT COMPRISING PAPER SURFACE SIZED WITH 0.05-1.4%, BASED ON THE DRY WEIGHT OF THE PAPER, OF BORIC ACID AND 0.1-4% OF A COPOLYMER SELECTED FROM THE GROUP CONSISTING OF STYRENE-MALEIC ANHYDRIDE COPOLYMER AND STYRENE-MALEIC ANHYDRIDE COPOLYMER, PART OF THE CARBOXYL OF WHICH HAS BEEN ESTERIFIED WITH A LOWER ALKYL GROUP.
 12. A METHOD OF PREPARING A HIGHLY STAIN RESISTANT PAPER WHICH COMPRISES TUB SIZING THE PAPER WITH AN AQUEOUS ALKALINE SOLUTION CONTAINING BORIC ACID AND A COPOLYMER SELECTED FROM THE GROUP CONSISTING OF STYRENEMALEIC ANHYDRIDE COPOLYMER AND STYRENE-MALEIC ANHYDRIDECOPOLYMER, PART OF THE CARBOXYL OF WHICH HAS BEEN ESTERFIED WITH A LOWER ALKYL GROUP. 